The papers in this Special Section present the latest results of research into the waterlogged later prehistoric site at Flag Fen, Peterborough. The landscape is almost flat and very low-lying, and the archaeological site consists of two main elements: a man-made timber platform and a kilometre-long alignment of posts, interpreted here as a defensive palisade. The site also has an important ritual component that continued into the Iron Age. Dendrochronology and other evidence indicates that the platform and posts were used for some 400 years, between about 1350 and 950 BC. This was a period of increasing wetness in the region.